Pants-type disposable diapers having a waist opening at the top end and a pair of leg openings in the lower portion have conventionally been used as one type of absorbent articles for receiving body waste discharged from a wearer. In front and rear parts of a pants-type disposable diaper that are located respectively on the belly and back sides of the wearer, a waist elastic member is provided along the edge of the waist opening. In a crotch part located between the front and rear parts, leg elastic members are provided along the edges of the pair of leg openings. In the front and rear parts, a middle elastic member is also provided between the waist elastic member and the leg elastic members in an up-down direction.
In a pants-type disposable diaper disclosed in Japanese Patent Application Laid-Open No. 2009-240694 (Document 1), front and rear parts located on the belly and back sides of a wearer are divided into a first expansible region that is located in the vicinity of the edge of a waist opening, a second expansible region that is located adjacent to the first expansible region and crosses a front end portion of an absorptive chassis, and third expansible regions that are located adjacent to the second expansible region and on both sides of the absorptive chassis. Setting the elongation stress of the second expansible region to be equal to or greater than that of the first expansible region suppresses the formation of creases in the second expansible region and the front end portion of the absorptive chassis due to the effect of elongation of the first expansible region when the wearer bends forward.
In pants-type absorbent articles disclosed in Japanese Patent Application Laid-Open Nos. 2009-125088 (Document 2) and 2009-125087 (Document 3), front and rear parts are divided into four strip-like regions of the same width that extend in the width direction, the four strip-like regions being referred to respectively as a first region, a second region, a third region, and a fourth region in order from the top. In the pants-type absorbent article disclosed in Document 2, the contractile forces in the respective regions are set such that the second region has a greater contractile force than those of the first and third regions, and the fourth region has a greater contractile force than that of the third region. In this way, setting a greater contractile force in the second and fourth regions where the wearer has bones that protrude to the surface of his or her body suppresses slipping off of the absorbent article, and setting a smaller contractile force in the first region that shifts greatly due to movement of the wearer makes the absorbent article more comfortable to wear. In Document 3, which aims to provide a pants-type disposable diaper capable of preventing slipping-off and being very comfortable to wear, the second and fourth regions are set to have an average contractile force greater than that of the third region, the fourth region on the belly side is set to have a contractile force greater than that of the forth region on the back side, and the second region is set to have an average contractile force greater than that of the first region.
In a disposable diaper disclosed in Japanese Patent Application Laid-Open No. 2010-69023 (Document 4), a front part is divided from the waist opening side into a first expansible region, a second expansible region, and a third expansible region, a rear part is divided from the waist opening side into a fourth expansible region, a fifth expansible region, and a sixth expansible region, and the elongation stresses of the respective expansible regions has the following correlation: sixth expansible region>second expansible region>third expansible region≥fifth expansible region>first expansible region, and sixth expansible region>second expansible region>third expansible region fifth expansible region>fourth expansible region.
In a pants-type disposable diaper disclosed in Japanese Patent Application Laid-Open No. 2001-178770 (Document 5), front and rear parts are divided from the waist opening side into a waist section, an upper side section, and a lower side section, and elastic expansion forces of the respective sections has the following correlation: lower side section≥upper side section>waist section.
In a pants-type disposable diaper disclosed in Japanese Patent Application Laid-Open No. 2006-61682 (Document 6), when the disposable diaper is worn, a first region located between a waist opening and leg openings has the highest pressure applied thereto, the waist opening has the second highest pressure applied thereto, and a second region located between the first region and the leg openings has the lowest pressure applied thereto. Such a structure not only effectively prevents the diaper slipping off when being worn, but also effectively prevents liquid leakage because the diaper fits the body of a wearer closely without discomfort.
Incidentally, in pants-type disposable diapers, a pair of strip projecting parts, each projecting laterally from a line of connection between front and rear parts, is formed when the front and rear parts are joined to each other on both right and left sides. The strip projecting parts are less flexible than the other parts of the disposable diaper because they are formed by joining laminated sheet members such as nonwoven fabric by thermal compression bonding, for example. Thus, in a state where the disposable diaper is worn, the upper end portions of the strip projecting parts may cut into the body of the wearer and make the wearer uncomfortable due to contraction of a waist elastic member provided in a waist region extending along the edge of the waist opening.
Documents 1 to 6 have proposed to reduce the contractile force in the waist region to smaller than that in the other region, but it is necessary to maintain the contractile force in the waist region at a certain level or higher in order to prevent the disposable diaper from slipping off the wearer. Thus, with the structures as disclosed in Documents 1 to 6, the upper end portions of the strip projecting parts will still cut into the body of a wearer.